Re: Apple II drives and automatic monitor degaussing

["Michael J. Mahon" <mjmahon@aol.com>]

jsnospam@cimmeri.com wrote:
> On Feb 3, 3:52 pm, "Michael J. Mahon" <mjma...@aol.com> wrote:
> << Demagnetizing disk heads is not necessary, so there is no real
> benefit. >>
>
> You know, I never thought to ask before, but why do they not require
> demag-ing just as tape heads do?

Alex answered this part.

And it's just as well that it isn't an issue, since writing results
in saturating the head in both magnetic directions, rendering any
previous magnetization immaterial.

> << The real issue is interference with disk reading from the stray
> fields from the monitor deflection yoke and sweep circuits....
> Intervening magnetic shielding is also a major factor.>>
>
> ** The monitor internals are fully enclosed in a grounded metal
> cage... and the drives themselves are somewhat shielded internally
> with cage-like parts.   Do you think these shields help with the
> fields you are talking about?

It certainly helps.  But in some cases ;-) it may not help enough
to prevent read errors.

> ** The other thing I'm thinking of doing is just disconnecting the
> internal deguass coil as I know how to degauss manually, and I've
> never really had much need to degauss anyway.

I wouldn't worry about the degauss coil, since it is only energized
(significantly) for the first second or two after you turn on the
monitor.  Is your drive failing on a power-up boot?

If you don't move your monitor much, or change its orientation, you
may not need the degauss operation, but it seldom does harm, and
you *will* need it at some point.

-michael

NadaNet networking for Apple II computers!
Home page:  http://members.aol.com/MJMahon/

"The wastebasket is our most important design
tool--and it's seriously underused."